The invention relates to a method of treating a base material for obtaining one or more specific properties by diffusing a specific substance into the base material, said substance directly or indirectly inducing the specific property or properties.
Diffusing a foreign material into a base material in order to modify it, is known per se. Among other things, doping of semiconductors in order to give them a p- or n-type conductivity is known. There, diffusing of xe2x80x9cimpuritiesxe2x80x9d takes place from the gas phase.
In U.S. Pat. No. 5,427,662 corresponding to the international patent application WO92/20728 (corresponding to Dutch patent application 91 00815) from the same inventor, a method is disclosed for producing an ionomer. According to said method a plastic is provided, an electrically conducting medium placed in contact with a plastic surface of said plastic, and an electrical field applied over the plastic surface. By the influence of the electrically field, in the presence of the electrically conducting medium, groups are radicalized or ionized from external and/or internal plastic surface in the direction of the electrical field in the plastic, which groups are converted as a result for instance of oxidation reactions into for example carboxylic acids or sulphonic acids. As an electrically conducting medium both liquids and gases can be used. If the electrically conducting medium has an inherent insufficient activity, reactive components can be added to the medium and/or the plastic such as reactive gases, for promoting the radicalxe2x80x94forming or ion-forming reactions as well as oxidation reactions. In case the electrically conducting medium is a liquid such as water and ammonia, or an organic liquid such as methanol and ethanol, metal salts can be added to the conductive medium as reactive components. Metal ions can accelerate the growth of hydrophilic channels in the plastic, possibly due to a catalytic acceleration of the oxidation reactions.
According to the present invention it is now found that by means of an electric field applied over an electrically conducting medium in contact with a base material, it is possible to diffuse all kinds of specific substances into the base material for inducing new or changed properties other than ionomeric properties. Such properties comprise the physical structure, the optical properties, selective permeability for gases (membrane action), chemical properties, thermal properties, mechanical properties such as bending and tensile strength, electric properties and magnetic properties.
Accordingly the present invention provides a method of treating a base material for obtaining one or more specific properties, excluding ionomeric properties, by diffusing a specific substance into the base material, said substance directly or indirectly inducing the specific property or properties, characterized in that the base material is contacted with an electrically conductive medium, and that the specific substance is diffused into and/or reacts in the base material by means of an electric field being applied across the total of said base material, electrically conductive medium and specific substance.
It has appeared that an electric field is capable of causing substances to diffuse faster into base materials situated in said field. Faster diffusion is also understood to comprise injection. It is also understood to comprise a process in which electrochemical reactions at the base material play an essential role in the diffusion and inducing, casu quo changing, of properties. In all cases an electric field should be applied over the base material at or near the position where the change is intended. The result of such a diffusion is that the diffused substance leads to a novel or changed property. It is also possible that diffusion itself gives novel or changed properties to the base material in which the introduced substance itself does no longer make any essential contribution to said new or changed property. Said diffusion or injection roughly occurs along the field""s electric field lines. The moving spirit behind this is a yes or no temporary increase of the conductivity, the capacity, or a combination of both, in said base material.